Feb. 18, 2011

Beckett has been fascinated by batteries for as long as I can remember, so his latest suggestion for a science topic should not have been a surprise. Beckett wanted to know how toys work. We talked about the mountain of toys he has and about the energy makes them work -- whether the energy comes from him pushing a car or throwing an airplane, or from batteries or rubber bands. This led naturally enough to a discussion about potential energy and kinetic energy.

Potential Energy
Potential energy is stored energy, energy that is waiting to be used, and it comes in many forms. The most basic form of potential energy is provided by gravity -- an object that is not at rest on the surface of the earth probably has some potential gravitational energy in it. We pulled out one of Rowan's toys and asked him to demonstrate. When the ball is poised at the top of the ramp, it has potential energy. Gravity is pulling it down, but until it is free to move, the energy is being stored in it. As soon as Rowan lets go, gravity begins pulling the ball down, and it rolls down the ramp until it hits the bottom. The energy it has while it is rolling is called kinetic energy. You can repeat this experiment with our without Rowan's 'gravity dance.'

Spring Tension
Next we talked about wind-up toys. This type of toy stores energy in a coil of metal in a form called spring tension. Winding the toy places a spring under tension. The metal of the spring is flexible, but it has a manufactured coil shape that it returns to when the tension is released. You can see examples of this everywhere -- bend a stick or plastic spoon without breaking it and it will snap back to its original shape, or yank a rubber band from normal size to three times its size and let it snap. Even when you gently fold (without creasing) one end of a sheet of paper to the other end and let go, the paper will slowly unfold back to flat. (There is not a lot of energy there, but it is there.)

Wind-up toys generally have a tiny coil spring that can hold enough energy to move a small toy. Beckett has a lot of toys that use this type of potential energy -- bath toys that swim, little robots that walk, and lots of cars. We found a little plane with wind up wheels to demonstrate.

Inertia
Finally, we dug through the pile of toys and found a car with a flywheel, also called an inertia wheel. This toy uses a large rotating mass and a set of gears to translate the movement of the large rotating mass into forward motion for the car. Without getting too Einstein-y about it, the large mass of the flywheel is stepped down with a set of gears to propel the car. The flywheel 'stores' energy using the law of conservation of energy, which says that energy cannot be created or destroyed, but can only change its form. In this case, when the flywheel is set in motion, it has a certain amount of energy that can be harnessed using the gears and transferred to the wheels.

Other Energy Sources
The boys and I also talked about the many toys they both have that are powered by batteries. The batteries store potential energy chemically and release the energy over time as the electrical circuit is completed. The chemistry is far too complicated to explain here, so we looked at other ways of creating electricity. We started with Beckett's solar powered car, which uses photovoltaic cells to turn solar energy into electricity to move the car. This is fairly straightforward: the photons of light hit the photo-cell, where they are converted into electrons.

Next, we looked at other ways to make electricity -- lemon and potato batteries, for example -- that use a simple chemical reaction to generate electricity. The lemon stores potential energy in the acid that can be released by inserting two different metals and starting a reaction. The lemon also stores another kind of potential energy -- in the form of calories that can be eaten, changed by a different chemical reaction, and consumed in our bodies as fuel.

There are other forms of energy used by toys -- Beckett and Rowan both have toys that use magnetic energy in one form or another, and most balls use elastic potential energy to bounce along with gravity. Some toys use light energy to play. The best toys require a large dose of kid energy to play. What kinds of toys do you have, and what kind of energy do they need?

A Quick Update on Groundhog Day
We've had a week of unusually warm weather, so I wanted to share an update on Puxsutawney Phil because Beckett asked about him this morning on the way to school. "Dad," he said, "does a groundhog really decide when spring is?"

I tried to think of a 'science' question I could ask him to help him figure it out, but the best I could come up with was this: "Well, do you think a groundhog can control or predict the weather for the whole planet? "

This turned out to be exactly the right question, because he immediately brightened and smiled. "Obviously not," he said.

"And why not?" I asked.

"Because half the planet is in the dark during their nighttime, so no shadows!"

I thought this was a great answer with a certain kind of logic and even science to it. No light means no shadow, and no shadow means no prediction.

Be sure to ask a kid in your life if groundhogs really determine the weather. If you need help, you can check out our very first blog post here, and find out what really determines the seasons.

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Science Dad, AKA Vince Harriman, is a freelance writer living in Annapolis. His two sons, Beckett - 6 and Rowan - 2 1/2 ask him ‘why’ approximately 6,549 times a day.